In silicon devices such as insulated gate bipolar transistors (IGBTs), diodes, insulated gate field effect transistors (IGFETs), for example metal oxide semiconductor field effect transistors (MOSFETs) a number of requirements need to be met. Such requirements typically depend upon specific application conditions. Typically, trade-offs between linked characteristics such as, for example high electrical breakdown voltage and low on-state resistance have to be found. Avalanche breakdown events and undesired formation of inversion channels, for example at silicon to oxide interfaces that may occur during operation of the semiconductor device may have a negative impact on device robustness and device reliability.
As a typical base material for manufacturing a variety of such semiconductor devices, silicon wafers grown by the Czochralski (CZ) method, e.g. by the standard CZ method or by the magnetic CZ (MCZ) method or by the Continuous CZ (CCZ) method are used. In the Czochralski method, silicon is heated in a crucible to the melting point of silicon at around 1416° C. to produce a melt of silicon. A small silicon seed crystal is brought in contact with the melt. Molten silicon freezes on the silicon seed crystal. By slowly pulling the silicon seed crystal away from the melt, a crystalline silicon ingot is grown with a diameter in the range of one or several 100 mm and a length in the range of a meter or more. In the MCZ method, additionally an external magnetic field is applied to reduce an oxygen contamination level.
Growing of silicon with defined doping by the Czochralski method is complicated by segregation effects. The segregation coefficient of a dopant material characterizes the relation between the concentration of the dopant material in the growing crystal and that of the melt. Typically, dopant materials have segregation coefficients lower than one meaning that the solubility of the dopant material in the melt is larger than in the solid. This typically leads to an increase of doping concentration in the ingot with increasing distance from the seed crystal.
It is desirable to improve robustness and reliability of silicon semiconductor devices. It is further desirable to provide a wafer as a base material for such silicon semiconductor devices and to provide a method of manufacturing the wafer.